System information

Configuring IP Multicast Routing
8-1
Overview
The IP multicast routing environment allows a host to send packets to a group of hosts
called group members. Multicast packets delivered to group members are identified
by a single multicast group address and use best-effort reliability.
Hosts can be both senders and receivers. Any host, regardless of whether it is a
member of a group, can send to a group. However, only the members of a group
receive the message. A multicast address is chosen for the receivers in a multicast
group. Senders use that address as the destination address of a datagram to reach all
members of the group.
Multicast group membership is active; hosts can join and leave at any time. There is
no restriction on the location or number of members in a multicast group. A host can
be a member of more than one multicast group at a time.
How active a multicast group is and what members it has can vary from group to
group and from time to time, and a multicast group can be active for long or brief time
periods. Group membership can change constantly and have inactive members.
Multicast routing protocols, such as Protocol-Independent Multicast (PIM) and
Distance Vector Multicast Routing Protocol (DVMRP) are used to maintain
forwarding tables in order to forward multicast datagrams between routers on the
network. The BSR uses the Internet Group Management Protocol (IGMP) on a
specified interface to learn whether members of a group are present on their directly
attached subnetworks. Hosts join multicast groups by sending IGMP report messages.
Use the following sections in this chapter to configure IP multicast routing or display
IP multicast routing information on the BSR:
• Enabling IP Multicast Routing on the BSR
• Configuring PIM
• Configuring DVMRP
• Configuring IGMP on an Interface
• Managing IP Multicast Routing on the BSR
• Gathering IP Multicast Information